1. Field of the Invention
The present invention relates to a lens frame of a projection lens to be attached, for example, on a projector of a projection-type television.
2. Description of the Related Art
FIG. 7 shows a projector of a projection television wherein a lens barrel 10, in which a projection lens is incorporated, is supported by a barrel support portion 20 and the barrel support portion 20 is attached to a projection tube 40 through a coupler 30 for performing optical coupling. An image formed on a projection tube 40 is projected on a screen 50 through the projection lens incorporated within the lens barrel 10.
FIG. 5 shows an example of a conventional lens barrel and barrel support portion wherein a cylindrical lens barrel 10 is fitted into a cylindrical portion 20a of a barrel support portion 20, and a fixing portion 60 is attached to lens barrel 10 through a slot portion 20b slantedly formed through a cylindrical portion 20a.
As shown in FIG. 6, a fixing portion 60 is structured such that a screw 60a is fitted into a protrusion 10a through a wing nut 60b, a washer 60c, and a collar 60d. The protrusion 10a is formed on the side surface of the lens barrel 10 and a collar 60d is fitted in the slot portion 20b of the cylindrical portion 20a.
To focus the image formed on the projection tube 40 onto the screen 50, the lens barrel 10 is rotated within the barrel support portion 20 to cause the collar 60d to slide along the slot portion 20b so that the lens barrel 10 is rotatably displaced relative to the barrel support portion 20 with respect to the central axis of the cylindrical portion 20a.
Upon completion of the focusing of the image on the screen 50, the wing nut 60b is turned and tightened to force the lens barrel 10 against the cylindrical portion 20a of the barrel support portion 20 so as to fix the lens barrel 10 to the barrel support portion 20.
In the foregoing conventional configuration, however, there has been a problem in that the number of parts comprising the fixing portion 60 is so large that it takes along time to assemble the lens barrel 10 and the barrel support portion 20 because it is necessary to pass the screw 60a through the wing nut 60b, the washer 60c, and the collar 60d while, at the same time, to position the protrusion 10a of the lens barrel 10 so as to be coincident with the slot portion 20b of the cylindrical portion 20a so that the screw 60a can be properly fitted into the protrusion 10a of the lens barrel 10.
Further, even though the center of the lens barrel 10 coincides with that of the cylindrical portion 20a before fixing by the wing nut 60b as shown in FIG. 4(a), the central axis of the lens barrel 10 becomes displaced from that of the cylindrical portion 20a when fixing is performed by tightening the wing nut 60b because the portion of the lens barrel 10 adjacent to the fixing portion 60 is pulled toward the inner surface of the cylindrical portion 20a as shown in FIG. 4(b). This results in another problem in that, upon fixing the wing nut 60b, the central axis of the barrel support portion 20, which is fixed at a position optically set with respect to the coupler 30, is displaced from the central axis of the lens barrel 10, and consequently displaced from the optical axis of the projection lens incorporated within the lens barrel 10, so that the image forming performance of the projector deteriorates.